The present invention relates to an injection stretch-blow molding apparatus for the production of biaxially oriented hollow bodies from thermoplastic material, particularly polyester, including an injection-molding station, conditioning stations and a blow molding station, and means for transporting the performs between the individual stations.
Hollow bodies, for example bottles having threaded necks, are produced in such apparatus from injection-molded preforms. For this purpose, devices are known in which a mandrel arranged on a stepwise-rotating rotary disk passes in succession through an injection molding station, a conditioning station and a blow-stretching station, as shown in German Offenlegungsschrift No. 24 00 951. The biaxial orientation is produced by a stretching molding process which takes place within the blow mold. The preform, which has already cooled down in part at the injection molding station, must be thermally conditioned before the stretching process, i.e. it must be brought, within a relatively narrow tolerance, to a temperature suitable for the stretching process. The temperature distribution across the thickness of the wall of the preform increases quickly from the exterior boundaries of the wall to a high maximum in the center of the wall during a cooling process. But, the temperature distribution across the wall should be made as uniform as possible during the conditioning process. This is particularly necessary in the case of thick-walled preforms, such as those which must be used in the case of high stretching rates since some portion of the wall will otherwise remain outside the temperature range required for the stretching process. As a result, the cooling and conditioning times required are very large. In particular, the time necessary for the temperature-equalizing (conditioning) process in the preform wall due to slight unevennesses in temperature is up to twice the time necessary for the preform wall to cool in the mold during the injection molding process. For this reason, known injection and stretch-blowing apparatus are uneconomical, since their injection-molding and stretch-blowing stations are idle as much as half the time required for each complete cycle of the apparatus due to the time-consuming nature of the conditioning process.